The present invention relates generally to flexible fluid-type seals for pipe joints. More particularly, the invention relates to a gasket adapted for sealing bell-and-spigot type pipe joints.
The gasket disclosed herein is particularly adapted for use in the field of sewer pipe assemblies. However, it should be appreciated that the gasket design disclosed could be adapted for use in many other types of pipe joints as well.
Sewer pipe assemblies are generally made of plastic, polyethylene, metal, concrete, or other suitable materials. These are fabricated in many configurations and sizes to meet specific requirements and users"" preferences. In many such pipe assemblies, grooves are formed or recesses are provided in ribbed or corrugated types of pipe. Although a spigot, i.e., a male groove, is the dominant method employed for manufacturing sewer pipes, it is also possible that a formed groove in the bell, i.e., female pipe, can be utilized.
Some gaskets are integrally installed at the factory during fabrication of the sewer pipes while others are simply applied at the job site. For very large diameter concrete pipes, such as in storm and sanitary sewer systems, field installation of the gaskets is generally considered necessary.
Historically, piping systems have utilized polymeric gasket elements to provide resilient seals under various operating conditions. These include no internal pressure, no external pressure, working internal pressure, high external pressure, internal vacuum, or any combination of these. In each case, the gasket must maintain its ability to seal when quick changes occur in the pressures imposed on the gasket.
O-ring type gaskets have frequently been employed on large diameter pipe joints. The O-ring is typically mounted on the spigot, and the spigot is then pushed into the bell causing the O-ring to roll further onto the spigot until it reaches roughly the center of the pipe connection. Dirty or uneven surfaces, poor or improperly applied lubricants, misaligned pipes, and excessive force may cause the O-ring to distort non-uniformly, resulting in a weak seal, or even in a void through which fluids can flow. Some spigots include a circumferential groove or a single or a double offset shoulder to keep the O-ring from rolling as the pipes are interconnected. However, the diameter of the O-ring and its radial cross-section are usually greater than the depth of the groove or shoulder and the ring may still roll over the inside edge of the groove, become snagged or shear off segments of the O-ring as the spigot enters the bell.
Various gasket configurations have been used or suggested for overcoming these deficiencies. In order to provide self-alignment of the gasket, various gasket profiles have been developed. Typically, however, it is essential that the gasket be placed on the spigot in a desired orientation. That is, the gasket functions properly only when it is installed in a particular direction and cannot function if installed in a reverse or backwards manner. This has made it necessary for identification marks to be placed on the surface of the gasket for the purpose of distinguishing the front, or functional side, of the gasket profile from the back, or non-functional side. These stripes, printing, or color coding identifiers then become critical to the success or failure of the sealing system.
Sealing rings are known for sealing against fluid flow in both high and low pressure conditions in either direction. However, these sealing rings are not symmetrical and, therefore, can be installed incorrectly so that they will not seal properly.
There are symmetrical gaskets known for pipe joints. In commonly assigned U.S. Pat. No. 5,687,976, the entire contents of which are incorporated herein by reference, there is disclosed a symmetrical pipe joint gasket which includes an annular gasket body formed of a resilient material. The gasket includes a projection which extends radially away from the gasket body and an annular bore which is spaced away from the projection and which extends in the gasket body. Both the projection and the annular bore are located so that they are bisected by the centerline of the gasket profile. The gasket is insensitive to axial orientation and is able to react to pressure fluctuations. It will be recognized that the gaskets in accordance with the present invention have many of the attendant advantages of those disclosed in U.S. Pat. No. 5,687,976.
Certain problems exist in pipe manufacturing processes that result in conditions which provide ineffective sealing surfaces on the portion of the pipe which contacts the gasket. Such surface conditions include, pitting, crazing, raised bumps, waviness, flow marks, indentations, undispersed ingredients that come to the surface, and other such conditions where the pipe surfaces are not as smooth and consistent as desired. Such defects have the ability to cause a weak seal or a failure in the pipe joint, especially under conditions of internal pressures, external pressures, and internal vacuums. The failures occur since a pathway for liquid or air is created over, under, or around these surface imperfections.
Typically, many pipe joints are disqualified because of these results. Although the pipe may be otherwise fully acceptable, a minor imperfection on the sealing surface where the gasket contacts the pipe may result in a failure. If the gasket chosen cannot overcome this type of operating challenge, increased costs to the pipe producer, contractor, and ultimately the property owner, result.
Since minor surface conditions will arise in some of the many, many miles of pipe produced each year, a gasket sealing system which can overcome such defects would be of assistance to manufacturers and users of such piping installations by providing additional confidence and reliability and preventing major problems in the field.
Accordingly, it has been considered desirable to develop a new and improved gasket and pipe joint design which would overcome the foregoing difficulties and others while providing increased seal efficiency under higher operating pressures and other benefits.
According to the present invention, a gasket and pipe joint employing the same is provided having increased surface contact area and force.
In accordance with a first aspect of the present invention, a pipe joint comprises an outer pipe and an inner pipe inserted therein, wherein an annular groove is formed on one of the facing surfaces of the outer and inner pipes. A gasket positioned within the annular groove is adapted to provide a seal between the inner and outer pipes. The gasket comprises an annular gasket body formed of a resilient material and is symmetric about a centerline. The gasket body includes a base adapted to sealingly engage the groove, and has first and second projections or protrusions which run longitudinally along the gasket body and extend away therefrom. The first and second projections are located on opposed sides of the centerline. An annular bore, extending interiorly within the gasket body, comprises a central region bridging first and second spaced apart lobes, the bore being located in the gasket body such that it is bisected by the centerline thereof.
In a second aspect, a non-directional gasket which is insensitive to axial gasket orientation includes an annular gasket body which is formed of a resilient material, and which has an axial centerline and a base adapted to sealingly engage an annular groove on a pipe. First and second protrusions are symmetrically spaced apart about the centerline, and an annular bore extends in the gasket body. The bore includes a central region bridging first and second spaced apart lobes and is bisected by the centerline.
In a third aspect, a gasket for sealing an annular space in a bell-and-spigot pipe joint is provided which can be installed in an associated pipe joint in either direction along a longitudinal axis of the associated pipe joint. The gasket includes an annular elastomeric web having an inner peripheral surface formed to sealingly engage an outer periphery of an associated spigot. The web is symmetric about a centerline, and first and second elastomeric protrusions are symmetrically contraposed thereabout. The protrusions project outward from the web and are deflectable to engage an inner periphery of an associated bell.
In a fourth aspect of the present invention, a pipe joint which can accommodate surface defects in a joined sealing surface includes an outer pipe and an inner pipe inserted into the outer pipe, wherein one of the pipes comprises an annular groove. A gasket positioned within the annular groove is adapted to provide a seal between the outer pipe and the inner pipe. The gasket includes an annular gasket body formed of a resilient material and is transversely symmetrical about a centerline. The gasket includes a base portion adapted to sealingly engage the groove. First and second projections run along the gasket body and extend away therefrom the first and second projections being symmetrically spaced apart about the centerline and defining a recess therebetween. The gasket body is deformable to increase a surface contact area when the inner pipe is inserted into the outer pipe. An annular bore extends in the gasket body. The bore is adapted to equalize pressure in transverse fashion across the surface contact area when the inner pipe is inserted into the outer pipe.
In a fifth aspect, an improved method is provided for producing an annular gasket of a type for sealing a gap between an inner pipe and an outer pipe, wherein one of the pipes carries a gasket within an annular groove. The gasket comprises a first end engaging the groove and a second end disposed opposite the first end facing an aligned sealing surface of the other of the inner and outer pipes. The method includes producing an elongate gasket, formed from an elastically compressible material, as by molding or extrusion, and attaching opposite ends of the gasket. At the same time that the elongate gasket is being produced, first and second projections are provided running along the gasket body and extending away therefrom, and the first and second projections being symmetrically spaced apart about an axial centerline of the gasket. Also produced at the same time the gasket body is being produced is an annular bore extending in the gasket body, the bore comprising a central region bridging first and second spaced apart lobes, the bore being located in the gasket body such that it is bisected by the centerline.
In a sixth aspect, a method for increasing the surface contact area of a gasket sealing a space between an inner pipe segment and an outer pipe segment adapted to receive the inner pipe comprises forming, at the same time the gasket is formed, first and second projections running along the gasket and extending radially therefrom. The first and second projections are symmetrically spaced apart about a centerline of the gasket. At the same time the gasket is formed, an annular bore is formed in the gasket. The bore comprises a central region bridging first and second spaced apart lobes, the bore being located within the gasket body such that it is bisected by the centerline. An annular groove is formed on one of the inner and outer pipes and the gasket is installed therein such that it is positioned within the annular groove. The inner pipe is then inserted into the outer pipe to compress the gasket and to provide a sealing pressure between the inner and outer pipes.